[Bluez PATCH v3 0/2] Bluetooth: Fix scannable broadcast advertising on extended APIs

[Bluez PATCH v3 0/2] Bluetooth: Fix scannable broadcast advertising on extended APIs

[Daniel Winkler]

Hello Maintainers,

We have discovered that when userspace registers a broadcast
(non-connectable) advertisement with scan response data, it exposes a
limitation in the new extended MGMT APIs. At the time that the
parameters are registered with the controller, kernel does not yet have
the advertising data and scan response (coming in a separate MGMT call),
and will default to a non-scannable PDU. When the MGMT call for
data/scan response is received, the controller will either fail when we
request to set the scan response, or return success and not use it.

This series along with another in kernel will allow userspace to pass a
flag with the params request indicating if the advertisement contains a
scan response. This allows kernel to register the parameters correctly
with the controller.

The patch is tested with a scannable broadcast advertisement on Hatch
and Kukui chromebooks (ext and non-ext capabilities) and ensuring a
peripheral device can detect the scan response.

Best,
Daniel

Changes in v3:
    - Use helpers to determine scannable rather than generating earlier

Changes in v2:
    - Check kernel supports flag before setting it

Daniel Winkler (2):
  advertising: Create and use scannable adv param flag
  doc/mgmt-api: Update documentation for scan_rsp param flag

 doc/mgmt-api.txt  |  5 +++++
 lib/mgmt.h        |  1 +
 src/advertising.c | 24 +++++++++++++++++++++++-
 src/shared/ad.c   | 17 +++++++++++++++++
 src/shared/ad.h   |  2 ++
 5 files changed, 48 insertions(+), 1 deletion(-)

-- 
2.31.0.rc2.261.g7f71774620-goog

[Bluez PATCH v3 1/2] advertising: Create and use scannable adv param flag

[Daniel Winkler]

In order for the advertising parameters hci request to indicate that an
advertising set uses a scannable PDU, we pass a scannable flag along
with the initial parameters MGMT request. This flag is populated based
on the existence of any scan response data requested by the client.

Without this patch, a broadcast advertisement with a scan response will
either be rejected by the controller, or will ignore the requested scan
response. The patch is tested by performing the above and confirming
that the scan response is retrievable from a peer as expected.

Reviewed-by: Sonny Sasaka <sonnysasaka@chromium.org>
Reviewed-by: Miao-chen Chou <mcchou@chromium.org>

---

Changes in v3:
    - Use helpers to determine scannable rather than generating earlier

Changes in v2:
    - Check kernel supports flag before setting it

 lib/mgmt.h        |  1 +
 src/advertising.c | 24 +++++++++++++++++++++++-
 src/shared/ad.c   | 17 +++++++++++++++++
 src/shared/ad.h   |  2 ++
 4 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/lib/mgmt.h b/lib/mgmt.h
index 76a03c9c2..7b1b9ab54 100644
--- a/lib/mgmt.h
+++ b/lib/mgmt.h
@@ -507,6 +507,7 @@ struct mgmt_rp_add_advertising {
 #define MGMT_ADV_PARAM_TIMEOUT		(1 << 13)
 #define MGMT_ADV_PARAM_INTERVALS	(1 << 14)
 #define MGMT_ADV_PARAM_TX_POWER		(1 << 15)
+#define MGMT_ADV_PARAM_SCAN_RSP		(1 << 16)
 
 #define MGMT_OP_REMOVE_ADVERTISING	0x003F
 struct mgmt_cp_remove_advertising {
diff --git a/src/advertising.c b/src/advertising.c
index d76e97a74..4ea0e60ee 100644
--- a/src/advertising.c
+++ b/src/advertising.c
@@ -793,6 +793,22 @@ static uint8_t *generate_scan_rsp(struct btd_adv_client *client,
 	return bt_ad_generate(client->scan, len);
 }
 
+static bool adv_client_has_scan_response(struct btd_adv_client *client,
+						uint32_t flags)
+{
+	/* The local name isn't added into the bt_ad structure until
+	 * generate_scan_rsp is called, so we must check these conditions as
+	 * well.
+	 */
+	if (!(flags & MGMT_ADV_FLAG_LOCAL_NAME) &&
+			!client->name &&
+			bt_ad_is_empty(client->scan)) {
+		return false;
+	}
+
+	return true;
+}
+
 static int get_adv_flags(struct btd_adv_client *client)
 {
 	uint32_t flags = 0;
@@ -917,7 +933,13 @@ static int refresh_extended_adv(struct btd_adv_client *client,
 		flags |= MGMT_ADV_PARAM_TX_POWER;
 	}
 
-	cp.flags = htobl(flags);
+	/* Indicate that this instance will be configured as scannable */
+	if (adv_client_has_scan_response(client, flags) &&
+		client->manager->supported_flags & MGMT_ADV_PARAM_SCAN_RSP) {
+		flags |= MGMT_ADV_PARAM_SCAN_RSP;
+	}
+
+	cp.flags = cpu_to_le32(flags);
 
 	mgmt_ret = mgmt_send(client->manager->mgmt, MGMT_OP_ADD_EXT_ADV_PARAMS,
 			client->manager->mgmt_index, sizeof(cp), &cp,
diff --git a/src/shared/ad.c b/src/shared/ad.c
index 23c8c34f4..d40d15331 100644
--- a/src/shared/ad.c
+++ b/src/shared/ad.c
@@ -552,6 +552,23 @@ uint8_t *bt_ad_generate(struct bt_ad *ad, size_t *length)
 	return adv_data;
 }
 
+bool bt_ad_is_empty(struct bt_ad *ad)
+{
+	/* If any of the bt_ad fields are non-empty or don't have the default
+	 * value, then bt_ad_generate will return a non-empty buffer
+	 */
+	if (!ad->name &&
+		ad->appearance == UINT16_MAX &&
+		queue_isempty(ad->service_uuids) &&
+		queue_isempty(ad->manufacturer_data) &&
+		queue_isempty(ad->solicit_uuids) &&
+		queue_isempty(ad->service_data) &&
+		queue_isempty(ad->data)) {
+		return true;
+	}
+	return false;
+}
+
 static bool queue_add_uuid(struct queue *queue, const bt_uuid_t *uuid)
 {
 	bt_uuid_t *new_uuid;
diff --git a/src/shared/ad.h b/src/shared/ad.h
index 13adcb406..84ef9dee9 100644
--- a/src/shared/ad.h
+++ b/src/shared/ad.h
@@ -105,6 +105,8 @@ void bt_ad_unref(struct bt_ad *ad);
 
 uint8_t *bt_ad_generate(struct bt_ad *ad, size_t *length);
 
+bool bt_ad_is_empty(struct bt_ad *ad);
+
 bool bt_ad_add_service_uuid(struct bt_ad *ad, const bt_uuid_t *uuid);
 
 bool bt_ad_remove_service_uuid(struct bt_ad *ad, bt_uuid_t *uuid);
-- 
2.31.0.rc2.261.g7f71774620-goog

[Bluez PATCH v3 2/2] doc/mgmt-api: Update documentation for scan_rsp param flag

[Daniel Winkler]

This patch adds the new scannable flag to the Add Extended Advertising
Parameters MGMT API documentation.

Reviewed-by: Alain Michaud <alainm@chromium.org>
Reviewed-by: Sonny Sasaka <sonnysasaka@chromium.org>

---

Changes in v3: None
Changes in v2: None

 doc/mgmt-api.txt | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/doc/mgmt-api.txt b/doc/mgmt-api.txt
index 1736ef009..cab1fffc5 100644
--- a/doc/mgmt-api.txt
+++ b/doc/mgmt-api.txt
@@ -3632,6 +3632,7 @@ Add Extended Advertising Parameters Command
 		13	The Timeout parameter should be used
 		14	The Interval parameters should be used
 		15	The Tx Power parameter should be used
+		16	The advertisement will contain a scan response
 
 	When the connectable flag is set, then the controller will use
 	undirected connectable advertising. The value of the connectable
@@ -3708,6 +3709,10 @@ Add Extended Advertising Parameters Command
 	chosen by the controller. If the requested Tx Power is outside
 	the valid range, the registration will fail.
 
+	When flag bit 16 is enabled, it indicates that the subsequent request
+	to set advertising data will contain a scan response, and that the
+	parameters should set a PDU type that is scannable.
+
 	Re-adding an already existing instance (i.e. issuing the Add Extended
 	Advertising Parameters command with an Instance identifier of an
 	existing instance) will update that instance's configuration. In this
-- 
2.31.0.rc2.261.g7f71774620-goog

Re: [Bluez PATCH v3 0/2] Bluetooth: Fix scannable broadcast advertising on extended APIs

[Daniel Winkler]

Hi Maintainers,

Friendly reminder to review this V3 patch at your convenience.

Thanks!
Daniel


On Tue, Mar 16, 2021 at 3:50 PM Daniel Winkler <danielwinkler@google.com> wrote:
>
> Hello Maintainers,
>
> We have discovered that when userspace registers a broadcast
> (non-connectable) advertisement with scan response data, it exposes a
> limitation in the new extended MGMT APIs. At the time that the
> parameters are registered with the controller, kernel does not yet have
> the advertising data and scan response (coming in a separate MGMT call),
> and will default to a non-scannable PDU. When the MGMT call for
> data/scan response is received, the controller will either fail when we
> request to set the scan response, or return success and not use it.
>
> This series along with another in kernel will allow userspace to pass a
> flag with the params request indicating if the advertisement contains a
> scan response. This allows kernel to register the parameters correctly
> with the controller.
>
> The patch is tested with a scannable broadcast advertisement on Hatch
> and Kukui chromebooks (ext and non-ext capabilities) and ensuring a
> peripheral device can detect the scan response.
>
> Best,
> Daniel
>
> Changes in v3:
>     - Use helpers to determine scannable rather than generating earlier
>
> Changes in v2:
>     - Check kernel supports flag before setting it
>
> Daniel Winkler (2):
>   advertising: Create and use scannable adv param flag
>   doc/mgmt-api: Update documentation for scan_rsp param flag
>
>  doc/mgmt-api.txt  |  5 +++++
>  lib/mgmt.h        |  1 +
>  src/advertising.c | 24 +++++++++++++++++++++++-
>  src/shared/ad.c   | 17 +++++++++++++++++
>  src/shared/ad.h   |  2 ++
>  5 files changed, 48 insertions(+), 1 deletion(-)
>
> --
> 2.31.0.rc2.261.g7f71774620-goog
>

Re: [Bluez PATCH v3 0/2] Bluetooth: Fix scannable broadcast advertising on extended APIs

[Luiz Augusto von Dentz]

Hi Daniel,

On Mon, Mar 22, 2021 at 9:32 AM Daniel Winkler <danielwinkler@google.com> wrote:
>
> Hi Maintainers,
>
> Friendly reminder to review this V3 patch at your convenience.
>
> Thanks!
> Daniel
>
>
> On Tue, Mar 16, 2021 at 3:50 PM Daniel Winkler <danielwinkler@google.com> wrote:
> >
> > Hello Maintainers,
> >
> > We have discovered that when userspace registers a broadcast
> > (non-connectable) advertisement with scan response data, it exposes a
> > limitation in the new extended MGMT APIs. At the time that the
> > parameters are registered with the controller, kernel does not yet have
> > the advertising data and scan response (coming in a separate MGMT call),
> > and will default to a non-scannable PDU. When the MGMT call for
> > data/scan response is received, the controller will either fail when we
> > request to set the scan response, or return success and not use it.
> >
> > This series along with another in kernel will allow userspace to pass a
> > flag with the params request indicating if the advertisement contains a
> > scan response. This allows kernel to register the parameters correctly
> > with the controller.
> >
> > The patch is tested with a scannable broadcast advertisement on Hatch
> > and Kukui chromebooks (ext and non-ext capabilities) and ensuring a
> > peripheral device can detect the scan response.
> >
> > Best,
> > Daniel
> >
> > Changes in v3:
> >     - Use helpers to determine scannable rather than generating earlier
> >
> > Changes in v2:
> >     - Check kernel supports flag before setting it
> >
> > Daniel Winkler (2):
> >   advertising: Create and use scannable adv param flag
> >   doc/mgmt-api: Update documentation for scan_rsp param flag
> >
> >  doc/mgmt-api.txt  |  5 +++++
> >  lib/mgmt.h        |  1 +
> >  src/advertising.c | 24 +++++++++++++++++++++++-
> >  src/shared/ad.c   | 17 +++++++++++++++++
> >  src/shared/ad.h   |  2 ++
> >  5 files changed, 48 insertions(+), 1 deletion(-)
> >
> > --
> > 2.31.0.rc2.261.g7f71774620-goog
> >

Applied, thanks.

-- 
Luiz Augusto von Dentz